The present invention generally relates to copying apparatuses and more particularly, to a copying apparatus including an original scanning means including a reciprocating optical unit and a reciprocating original platform, in which relative positions of a leading edge of a copy paper sheet and a front end of an image to be copied are controlled in accordance with a time interval between a point of time at the start of scanning of the original scanning means and a point of time at the start of transport of the copy paper sheet.
Conventionally, it has been so arranged that when an image of an original document is copied onto a copy paper sheet, the image is shifted on the copy paper sheet from a position of the image on the original document. To this end, a method has been employed in which on the basis of a point of time of displacement of the original scanning means to the leading edge of the copy paper sheet, a point of time at the start of transport of the copy paper sheet is set in a time period during constant speed displacement of the original scanning means.
FIG. 3 is a view explanatory of the construction and operation of a movable optical system type copying apparatus. In FIG. 3, an optical unit is included by a first mirror 1, a second mirror 2 and a third mirror 3 and is displaced so as to scan an image of an original document (not shown) placed on an original platform 7. A photosensitive drum 6 is disposed below the optical unit and a paper start clutch PSC is disposed adjacent to the photosensitive drum 6. A copy paper sheet (not shown) is temporarily stopped by the paper start clutch PSC so as to be further conveyed at a predetermined timing. Characters L1 and L2 denote a circumferential distance between an exposure position P4 and a transfer position P5 of the photosensitive drum 6 and a distance between a position P6 of the paper start clutch PSC and the transfer position P5 of the photosensitive drum 6, respectively. In the copying apparatus of the above described arrangement, a timer (not shown) is actuated at the time of displacement of the first mirror 1 to a point P2 and the paper start clutch PSC is controlled upon lapse of a preset time of the timer such that the image of the original document can be shifted on the copy paper sheet through a maximum distance of (L1-L2) from a position of the image on the original document. The maximum distance of (L1-L2) is approximately 10 to 20 mm at most and thus, the image cannot be shifted on the copy paper sheet through a large distance from the corresponding position of the image on the original document. In the case where the image is copied onto the copy paper sheet by shifting the image on the copy paper sheet through a large distance from the position of the image on the original document, for example, centering copying is performed in which the image is copied onto a central portion of the copy paper sheet at a reduction ratio, it has been necessary to start scanning of the original scanning means upon lapse a predetermined time period after the start of transport of the copy paper sheet. In this case, timing control of the original scanning means is required to be performed in consideration of a time period except for the time period during constant speed displacement of the original scanning means, i.e. a time period during which the original scanning means is displaced from a home position to a reference position such as a front end of the original document.
However, since a scanning start position, i.e. a stop position of the original scanning means varies according to the previous scanning of the original scanning means, relative positions of the leading edge of the copy paper sheet and the front end of the image may change, thereby resulting in such a problem that the image cannot be accurately copied onto a predetermined position of the copy paper sheet.